SEED-COAT, &c. 



somewhat in their characters in different plants : those of 

 Ricinus may be taken as a good type. 



Having noted the hard, variously marked seed-coat, with the 

 wart-like swelling (aril) at the basal end, crack and remove it : 

 beneath it will be found the white oily mass of the endosperm. 

 Cut this through transversely, and with a razor wetted with 

 olive oil, or castor oil, cut thin sections from it, and mount in 

 the oil. Examine under a high power, and observe 



1. The thin cell-walls of the oval cells. f 



2. The numerous highly refractive aleurone-grains in each 

 cell ; each is of oval form, and a less highly refractive area is 

 seen at one end : this is the glojboid. 



3. The oily matrix in which the grains are embedded, this 

 being so transparent as to be hardly visible. 



Cut other sections with the razor wetted with alcohol, soak 

 them well in alcohol in a watch-glass to remove the oil, which 

 is soluble in alcohol, but more readily in ether : if ether be 

 used, wash it off afterwards with alcohol : mount in pure 

 glycerine : examine them under a high power, and observe 

 the appearance of the aleurone-grains as before when seen 

 in oil. 



i. Add water gradually, and watch its effect on the grains. 



1. The outer amorphous coat of the grain will swell, and 



become less highly refractive : thus there will be 

 disclosed 



2. The crystalloids, one, or rarely more, being included in 



each grain : these do not swell greatly with water, and 

 accordingly they retain their refractive power. 



3. The globoid will also be visible as before. 



ii. Add dilute potash solution : the amorphous coats and the 

 crystalloids will swell and dissolve, leaving the globoids. 



iii. Add strong acetic acid : the globoids will dissolve slowly. 



VI. Crystalloids. Crystalloids of cubical form are to be 

 found in the superficial tissues of the Potato. Cut tangential 

 sections from material hardened in alcohol, or in picric acid and 

 alcohol, and mount in pure glycerine and iodine : the cubical 

 crystalloids will be distinguished by their yellowish brown 

 staining. 



K 2 



